This invention relates to curable silicone resin compositions and to reactive silicon compounds useful in such curable compositions.
Curable silicone resins such as silsesquioxane resins are used in applications which take advantage of their heat and fire resistant properties, for example in fibre reinforced composites for electrical laminates and structural components for automotive, aircraft and naval use, and as interlayer dielectric materials and as abrasion resistant coatings. The resins cure to a rigid product. There is a need for silicone resin compositions of improved mechanical properties, such as increased flexural strength, fracture toughness, modulus and/or mechanical damping, without substantial loss of heat and fire resistance.
The toughness of a silicone resin has been increased by a rubber component, as described in U.S. Pat. No. 5,747,608 or U.S. Pat. No. 5,830,950 or by a silicone fluid as described in U.S. Pat. No. 5,034,061 or CA 691206.
GB 1119666 describes a resinous polymer comprising the reaction product of a compound of the formula (R)n(X)(3xe2x88x92n)Sixe2x80x94Rxe2x80x3xe2x80x94Si(X)(3xe2x88x92n)(R)n, wherein R is a monovalent hydrocarbon group, Rxe2x80x2 is phenylene, diphenylene or diphenylene oxide, X is hydroxy or alkoxy and n is 1 or 2 and a silane of the general formula (Rxe2x80x3)mSi(Y)4xe2x88x92m, wherein Rxe2x80x3 is a hydrocarbyl or substituted hydrocarbyl group, Y is alkoxy, acyloxy or hydroxy and m=0-2. GB1101589 describes a process for the production of an organosilicon resin by heating in the presence of a solvent a compound of the formula R1(R2)2Sixe2x80x94Rxe2x80x94Si(R2)2R1 where R is phenylene, diphenylene or diphenylene oxide, R1 is a monovalent hydrocarbon or substituted hydrocarbon group and R2 is alkoxy or hydroxy, with a compound of the formula R4(R3)2Sixe2x80x94Rxe2x80x94Si(R3)2R4 where each R3 is a monovalent hydrocarbon or substituted hydrocarbon group and R4 is acyloxy, alkoxy or hydroxy.
A curable silicone resin composition according to the present invention comprises (A) an uncured silicone resin having units of the formula (R*)a(R)bSiO(4xe2x88x92axe2x88x92b)/2, where each R* is a functional group capable of reacting with Sixe2x80x94OH and/or Si-alkoxy groups and each R is a nonfunctional monovalent hydrocarbon group, a+b is from 1.0 to 3.0 and each molecule of uncured silicone resin contains an average of at least two groups R*, and (B) a silanol or hydrolysable compound of the formula 
where each Rxe2x80x2 represents a hydroxyl group or a hydrolysable group; each Rxe2x80x3 represents hydrogen, a monovalent hydrocarbon which optionally is substituted, or a group within the above definition of Rxe2x80x2; and Ar is a substantially nonflexible linkage including at least one para-arylene moiety, so that the groups (Rxe2x80x2)2Rxe2x80x3Sixe2x80x94 are spatially separated.
The compound (B) reacts with the functional groups R* of the silicone resin to crosslink the resin (A) to a structure having improved mechanical properties and generally less brittle than that obtained by curing the resin (A) alone. The groups (Rxe2x80x2)2Rxe2x80x3Sixe2x80x94 are spatially separated by the nonflexible linkage Ar so that intramolecular self-reaction of the groups (Rxe2x80x2)2Rxe2x80x3Sixe2x80x94 is avoided.